Semiconductor device design system and method, and software product for the same

ABSTRACT

A software product including codes for the method of determining parasitic resistance and capacitance from a layout of an LSI is executed by a computer. The method is achieved by providing a plurality of patterns of a wiring structure which contains a target interconnection; and by producing a library configured to store parameters indicating the parasitic resistance and the parasitic capacitance in relation to the target interconnection to each of the plurality of patterns. The producing is achieved by calculating the parameters to a plurality of conditions corresponding to deviation in manufacture of the wiring structure for each of the plurality of patterns.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technique to design a semiconductordevice, and in particular, relates to a technique to perform an LPE(Layout Parameter Extraction) process for a layout of a semiconductordevice.

2. Description of the Related Art

In designing a semiconductor device by using a computer (CAD system),layout design is carried out based on a netlist (information showingconnection relationship between logic elements) after logic design iscarried out. After a layout is determined, various types of verificationprocesses are conducted to check whether the layout satisfies a designrule, or whether a device having the layout properly operates, and soon. An LPE (Layout Parameter Extraction) process is known as one processcarried out in the verification process.

In the LPE process, extraction of a parasitic resistance and a parasiticcapacitance (referred to as “parasitic RC” hereinafter) relevant to aninterconnection in the obtained layout is carried out. Such a parasiticRC is a parameter that can be determined only after the layout isdetermined, and is not included in the netlist. Therefore, an extractedparasitic RC is added to the netlist, and the netlist containing theparasitic RC (referred to as “netlist with parasitic RC” hereinafter) isgenerated. That is to say, a tool for carrying out the LPE processinputs a netlist and a layout data, and outputs a netlist with parasiticRC.

After that, a delay verifying process and a timing verifying process arecarried out for a device on the design by using the obtained netlistwith parasitic RC. When the result of the verifying process indicates a“fail” state, the above layout design process is carried out again.Then, the LPE process and the verifying process are again carried out.The above processes are repeated until the layout “passes” the verifyingprocess. If the result of the verifying process indicates a “passed”state, a final layout data is determined.

Japanese Laid Open Patent Application (JP-P2001-265826A) discloses atechnique related to the LPE process. In a circuit simulation devicedisclosed in Japanese Laid Open Patent Application (JP-P2001-265826A),layout information of an integrated circuit is stored in a first storagesection. Also, interconnection variations information is stored in asecond storage section. Process information showing a manufacturingprocess of an integrated circuit is stored in a third storage section.An interconnection resistance and capacitance extracting sectionextracts interconnection resistance and capacitance in which variationare taken into consideration based on the layout information, theinterconnection variations information, and the process information, andgenerates a netlist that includes the extracted interconnectionresistance and interconnection capacitance. A simulation section inputsthe generated netlist, and conducts a delay analysis of the integratedcircuit in consideration of the interconnection variations.

As stated above, the LPE process is an important process requiring highaccuracy to determine whether or not a designed semiconductor deviceproperly operates. Here, in an actual manufacturing process of asemiconductor device, a structure of an interconnection and so on maynot be manufactured as precisely as is intended. In other words, aninterconnection layer width, an interconnection layer thickness, aninterlayer insulating film thickness, and so on may possibly indicatevariations from desired values. Such a variation is referred to as a“process variation” hereinafter. The process variation affect a delay ina circuit. Since the process variation may be caused, it is possiblethat an actual product does not operate properly, even if a designedlayout passes an operation verifying process of the computer.

In the LPE process, therefore, it is desirable to extract the parasiticRC in consideration of the process variation. It is also desirable toconduct a verifying process for a plurality of netlists with parasiticRC in which the process variation is taken into consideration.Consequently, a layout data is produced that can cope with some extentof the process variation. If a product is manufactured based on thelayout data, a probability that the product is defective is reduced evenif the process variation is generated.

However, when the process variation is considered, time for carrying outthe LPE process and the delay verifying process is greatly increased, ascompared with a case where the process variation is not considered. Asstated above, the process variation include variations of a plurality ofparameters such as the interconnection layer width and the interlayerinsulating film thickness, and the number of combinations of thevariations is huge. It is virtually impossible to extract the parasiticRC and carry out the delay verifying process for all the combinations.The above conventional example (Japanese Laid Open Patent Application(JP-P2001 -265826A)) gives suggestion of the LPE process and theverifying process taking the process variation into consideration.However, the conventional example does not describe a specific method ofreducing the time for the LPE process and the verifying process. Atechnique is demanded that can reduce the time for semiconductor devicedesign while considering the process variation.

SUMMARY OF THE INVENTION

An aspect of the present invention relates to a computer-readablesoftware product including codes, executed by a computer, for a methodof determining parasitic resistance and capacitance from a layout of anLSI. In this case, the method is achieved by providing a plurality ofpatterns of a wiring structure which contains a target interconnection;and by producing a library configured to store parameters indicating theparasitic resistance and the parasitic capacitance in relation to thetarget interconnection to each of the plurality of patterns. Theproducing is achieved by calculating the parameters to a plurality ofconditions corresponding to deviation in manufacture of the wiringstructure for each of the plurality of patterns.

Here, the plurality of conditions includes a 0^(th) condition to asecond condition, and a desired width and desired film thickness of thetarget interconnection are W₀ and T₀, respectively, standard deviationsof a distribution of the width of the target interconnection and adistribution of the film thickness thereof are σ_(w) and σ_(T),respectively, and the width W and the film thickness T in actualmanufacture of the target interconnection are expressed, by usingcoefficients α_(W) and α_(T), asW=W ₀+α_(W)*α_(W)andT=T ₀+α_(T)*σ_(T).In this case, the 0^(th) condition is a case where the width W and thefilm thickness T are W₀ and T0, respectively, the first condition is acase where a delay in the target interconnection is maximized under acondition that α_(W) ²+α_(T) ² is constant, and the second condition iswhen the delay in the target interconnection is minimized under thecondition that α_(W) ²+α_(T) ² is constant.

Also, in case of the first condition, one of the parasitic resistance ofand the parasitic capacitance related to the target interconnection ismaximized, and the other is minimized, and in case of the secondcondition, the one is minimized and the other is maximized.

Also, the plurality of conditions further contains a third condition anda fourth condition, and a deviation of another factor which relates tothe delay is ranged from +σ₀ to −σ₀. The first condition is the casewhere the delay is maximized under the condition that the deviation ofthe another factor is one of +σ₀ and −σ₀ and α_(W) ²+α_(T) ² isconstant, and the third condition is the case where the delay ismaximized under the condition that the deviation of the another factoris the other of +σ₀ and −σ₀ and α_(W) ²+α_(T) ² is constant. The secondcondition is the case where the delay is minimized under the conditionthat the deviation of the another factor is one of +σ₀ and −σ₀ and α_(W)²+σ_(T) ² is constant, and the fourth condition is the case where thedelay is minimized under the condition that the deviation of the anotherfactor is the other of +σ₀ and −σ₀ and α_(W) ²+α_(T) ² is constant.

Also, the coefficients α_(W) and α_(T) in the first condition are equalto the coefficients α_(W) and α_(T) in the third condition, and thecoefficients α_(W) and α_(T) in the second condition are equal to thecoefficients α_(W) and α_(T) in the fourth condition.

In this case, a center resistance value as a value of the parasiticresistance and a center capacitance value as a value of the parasiticcapacitance are stored in a library as the parameter to the 0thcondition. A ratio β_(R) of the parasitic resistance to the centerresistance and a ratio β_(C) of the parasitic capacitance to the centercapacitance value are stored in the library as the parameter to each ofthe first to fourth conditions.

Also, the method may be achieved by further reading a netlist of theLSI; reading a layout data indicating the layout of the LSI; calculatingthe parasitic resistance and the parasitic capacitance in each of theplurality of conditions to each of the interconnections contained in thelayout by referring to the parameters stored in the library; andgenerating a netlist with parasitic RC by adding the calculatedparasitic resistance and the calculated parasitic capacitance to thenetlist.

Also, the method may be achieved by further reading a netlist of theLSI; reading a layout data indicating the layout of the LSI; calculatingthe parasitic resistance and the parasitic capacitance in each of theplurality of conditions to each of the interconnections contained in thelayout by referring to the center resistance value, the centercapacitance value, and the ratios β_(R) and β_(C) stored in the library;and generating a netlist with parasitic RC by adding the calculatedparasitic resistance and the calculated parasitic capacitance to thenetlist.

In this case, the calculating may be achieved by calculating theparasitic resistance and the parasitic capacitance in each of the firstto fourth conditions by multiplying the ratios β_(R) and β_(C) by thecenter resistance value and the center capacitance value, respectively.

Also, the calculating may be achieved by generating correction ratiosβ_(R)′ and β_(C)′ by correcting the ratios β_(R) and β_(C) based on aconfiguration of a node; and calculating the parasitic resistance andthe parasitic capacitance in each of the first to fourth conditions bymultiplying the correction ratios β_(R)′ and β_(C)′ by the centerresistance value and the center capacitance value, respectively.

In this case, when the node comprises a group of interconnections ineach of N interconnection layers (N is a natural number), a summation oflengths of the interconnections in the group is Li (i is an integerequal to or more than 1 and equal to or smaller than N), and the ratioβ_(C) and the correction ratio β_(C)′ are the following equation:β_(C)′=1+(β_(C)−1)γ_(C)a parameter γ_(C) satisfies the following equation:${\gamma\quad}_{C} = {\sqrt{\sum\limits^{N}L_{i}^{2}}/{\sum\limits^{N}L_{i}}}$

Also, when the interconnection groups are connected in series in thenode, and the ratio β_(R) and the correction ratio β_(R)′ are thefollowing equation:β_(R)′=1+(β_(R)−1)γ_(R)the parameter γ_(R) satisfies the following equation:$\gamma_{R} = {\sqrt{\sum\limits^{N}L_{i}^{2}}/{\sum\limits^{N}L_{i}}}$

Also, when the interconnection groups is branched in the node, a subinterconnection group in n interconnection layer (n is an integer equalto or more than 1 and equal to or smaller than N) is connected in seriesto one interconnection in the interconnection group, a summation oflengths of the interconnections in the sub interconnection group is Lj(j is an integer equal to or more than 1 and equal to or smaller thann), the ratio β_(R) and the correction ratio β_(R)′ to the oneinterconnection are the following equation:β_(R)′1+(β_(R)−1)γ_(R)the parameter γ_(R) satisfies the following equation:$\gamma_{R} = {\sqrt{\sum\limits^{n}L_{j}^{2}}/{\sum\limits^{n}L_{j}}}$

In this case, when a plurality of the correction ratios β_(R)′ arecalculated to the one interconnection, the largest one of the pluralityof correction ratios β_(R)′ is adopted.

Also, the largest one of a plurality of the correction ratios β_(C)′ isadopted as a coupling capacitance between the nodes.

Another aspect of the present invention relates to a computer-readablesoftware product includes codes, executed by a computer, for a method ofdetermining parasitic resistance and capacitance from a layout of anLSI, by referring a library, wherein a wiring structure which contains atarget interconnection is a pattern, and the library stores parametersindicating the parasitic resistance and the parasitic capacitance inrelation to the target interconnection to a plurality of conditions forvariation in manufacture of the wiring structure with respect to each ofa plurality of the patterns. The method is achieved by reading a netlistof the LSI; by reading a layout data indicating the layout of the LSI;by calculating the parasitic resistance and the parasitic capacitance ineach of the plurality of conditions to each of the interconnectionscontained in the layout by referring to the parameters stored in thelibrary; and by generating a netlist with parasitic RC by adding thecalculated parasitic resistance and the calculated parasitic capacitanceto the netlist.

Here, a desired width and desired film thickness of the targetinterconnection are W₀ and T₀, respectively, standard deviations of adistribution of the width of the target interconnection and adistribution of the film thickness thereof are σ_(W) and σ_(T),respectively, and the width W and the film thickness T in actualmanufacture of the target interconnection are expressed, by usingcoefficients α_(W) and α_(T), asW=W ₀+α_(W)*σ_(W)andT=T ₀+α_(T)*σ_(T).The plurality of conditions comprises a 0^(th) condition to a secondcondition, and the 0^(th) condition is a case where the width W and thefilm thickness T are W₀ and T0, respectively. The first condition is acase where a delay in the target interconnection is maximized under acondition that α_(W) ²+α_(T) ² is constant, and the second condition iswhen the delay in the target interconnection is minimized under thecondition that α_(W) ²+α_(T) ² is constant.

Also, the plurality of conditions further contains a third condition anda fourth condition, and a deviation of another factor which relates tothe delay is ranged from +σ₀ to −σ₀. The first condition is the casewhere the delay is maximized under the condition that the deviation ofthe another factor is one of +σ₀ and −σ₀ and α_(W) ²+α_(T) ² isconstant, and the third condition is the case where the delay ismaximized under the condition that the deviation of the another factoris the other of +σ₀ and −σ₀ and α_(W) ²+α_(T) ² is constant. The secondcondition is the case where the delay is minimized under the conditionthat the deviation of the another factor is one of +σ₀ and −σ₀ and α_(W)²+α_(T) ² is constant, and the fourth condition is the case where thedelay is minimized under the condition that the deviation of the anotherfactor is the other of +σ₀ and −σ₀ and α_(W) ²+α_(T) ² is constant.

Also, a center resistance value as a value of the parasitic resistanceand a center capacitance value as a value of the parasitic capacitanceare stored in a library as the parameter to the 0th condition, and aratio β_(R) of the parasitic resistance to the center resistance and aratio β_(C) of the parasitic capacitance to the center capacitance valueare stored in the library as the parameter to each of the first tofourth conditions.

In still another aspect of the present invention, a method ofmanufacturing a semiconductor device which has a plurality of wiringlayers, is achieved by determining design criteria, and a manufacturingcondition of the semiconductor device; by carrying out layout design ofthe semiconductor device based on functional specification and thedesign criteria to produce a layout data; by estimating processvariations of width and thickness of each of interconnections for everywiring layer from the layout data based on the design criteria and themanufacturing condition; by determining an interconnection delayaffected by a specific condition of the process variations for everywiring layer; by repeating correction of the layout data, the estimationand the determination until the determined interconnection delay meetsthe function specification, to produce a final layout data; and bymanufacturing the semiconductor device based on the final layout dataand the manufacture condition. The determining an interconnection delayis achieved by determining a variation of the interconnection delay byusing of parasitic resistance and parasitic capacitance for every wiringlayer through statistical relaxation in which the process variations ofwidth and thickness of each of interconnections are independent betweenthe plurality of wiring layers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration of a semiconductordevice design system of the present invention;

FIG. 2 is a flow chart showing an operation of the semiconductor devicedesign system of the present invention;

FIG. 3A is a cross-sectional view showing one pattern of aninterconnection structure;

FIG. 3B is a cross-sectional view showing another pattern of theinterconnection structure;

FIG. 4 is a conceptual diagram showing a parasitic RC extractingprocess;

FIGS. 5A and 5B are conceptual diagrams showing a netlist and a netlist14 with parasitic RC, respectively;

FIGS. 6A and 6B are conceptual diagrams of cross-sectional structuresshowing process variation;

FIG. 7 is a conceptual diagram showing a method of determining cornerconditions according to the present invention;

FIG. 8 is a graph showing dependence of a delay time on an angle θ;

FIG. 9 is a conceptual graph showing corner conditions;

FIG. 10A is a graph showing dependency of parasitic resistance on theangle θ;

FIG. 10B is a graph showing dependency of parasitic capacitance on theangle θ;

FIG. 11 is a table showing the corner conditions in the presentinvention;

FIG. 12 is a flow chart showing a method of building up an RC library inthe present invention;

FIG. 13 is a table showing a RC library in the present invention;

FIG. 14 is a flow chart showing an LPE process in the present invention;

FIG. 15 is a conceptual diagram showing an extracting process ofparasitic RC in a first embodiment of the present invention;

FIG. 16 is a conceptual diagram showing an extracting process of theparasitic RC in a second embodiment of the present invention;

FIGS. 17A and 17B are conceptual diagrams showing an example of acorrection process in the second embodiment of the present invention;

FIG. 18 is a conceptual diagram showing another example of thecorrection process in the second embodiment of the present invention;

FIG. 19 is a conceptual diagram showing another example of thecorrection process in the second embodiment of the present invention;and

FIG. 20 is a conceptual diagram showing another example of thecorrection process in the second embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a semiconductor device design system of the presentinvention with reference to the attached drawings.

FIG. 1 is a block diagram showing a configuration of the semiconductordevice design system of the present invention. The semiconductor devicedesign system 1 is realized by a computer system (CAD: Computer AidedDesign). The semiconductor device design system 1 is provided with astorage unit 10, a processing unit 20, an LPE tool 30, a verifying tool40, an input unit 50, and a display unit 60.

The storage unit 10 is realized by a hard disk unit, for example, andconfigured to store an RC library 11, a netlist 12, a layout data 13, anetlist with parasitic RC 14, and an interconnection length data 15. Asdescribed later in detail, the RC library 11 is referred to at the timeof a LPE process, showing a parameter (referred to as an “RC parameter”hereinafter) relevant to a parasitic capacitance and a parasiticresistance of an interconnection (referred to as a “parasitic RC”hereinafter). The netlist 12 is a data showing connection relationshipbetween logic elements in a semiconductor device (LSI) under design. Thelayout data 13 shows a layout of the LSI under design. The layout data13 is generated by an automatic layout tool (not shown), and is storedin the storage unit 10. The netlist with parasitic RC 14 is a netlisthaving a parasitic RC obtained by LPE process to be mentioned later. Theinterconnection length data 15 shows a length of each interconnection inthe layout.

The processing unit 20 can access the storage unit 10. The LPE tool 30is a computer program (software product) executed by the processing unit20. The LPE tool 30 is provided with a library building section 31having a function of building up the RC library 11, and an RC extractingsection 32 having a function of carrying out the LPE process. Theverifying tool 40 is a computer program executed by the processing unit20, having a function of carrying out an operation verifying process(delay verifying process and timing verifying process) of the designedLSI.

As the input unit 50, a key board and a mouse are exemplified. A user(designer) can input various data and commands by using the input unit50, while viewing information displayed on the display unit 60. By usingthe semiconductor device design system 1 described above, the LPEprocess and the operation verifying process are carried out.

FIG. 2 is a flow chart showing an operation of the semiconductor devicedesign system 1 of the present invention. The overall flow of thepresent invention is briefly surveyed by referring to FIG. 2. Details ofthe present invention are described later.

The processing unit 20 carries out a process shown below in accordancewith commands of the LPE tool 30 and the verifying tool 40.

Step S10:

First of all, the RC library 11 is built up by the library buildingsection 31 in the LPE tool 30. The RC library 11 stores an RC parametershowing the parasitic RC of an interconnection (wiring) from which theRC parameter should be extracted (referred to as “targetinterconnection” hereinafter). As the RC parameter, a value of theparasitic RC itself may be stored, or a ratio of the parasitic RC to apredetermined reference value may be stored. The RC parameter iscalculated for each of various interconnection layers, various shape(width and thickness) of the target interconnection, and various typesof interconnection environment around the target interconnection. Suchshape and peripheral interconnection environment are referred to as a“pattern (interconnection structure or wiring structure)” hereinafter.

FIGS. 3A and 3B illustrate various patterns, showing variousinterconnection structures including a target interconnection 70. Thepattern is shown in a cross-sectional structure. In FIGS. 3A and 3B, aplurality of interconnection layers M1 to M3 are shown as examples.Also, the target interconnection 70 is formed in the interconnectionlayer M2, for example. Another interconnection 71 is formed around thetarget interconnection 70, and an interlayer insulating film 72 isformed between the interconnection layers. The shape (width andthickness) and peripheral environment of the target interconnection 70are different between FIGS. 3A and 3B, and the parasitic RC of thetarget interconnection 70 is also different.

The library building section 31 automatically generates various possiblepatterns, and calculates (simulates) the parasitic RC for each of thevarious patterns. The calculated parasitic RC (RC parameter) is storedin the RC library 11 in the storage unit 10. That is, the RC library 11shows the RC parameters for the various patterns. Here, according to thepresent invention, the RC library 11 shows a plurality of RC parameterunder “a plurality of conditions” for a single pattern. The plurality ofconditions correspond to various types of variation at the manufacturing(process variation). The plurality of conditions will be described laterin detail. Additionally, the RC library 11 just needs to be carried outonly once in advance for one technology (process). The same RC library11 is used for all the products that are based on the same technology.

Step S20:

A layout of an LSI that corresponds to the netlist 12 is determined byan automatic layout tool and manual operation not shown. The layout data13 showing the determined layout is stored in the storage unit 10.

Step S30:

Next, the LPE process (parasitic RC extracting process) is carried outby the RC extracting section 32 in the LPE tool 30. First, the RCextracting section 32 (the processing unit 20) reads the netlist 12 andthe layout data 13 stored in the storage unit 10.

Step S40:

Secondly, the RC extracting section 32 extracts (calculates) theparasitic RC for every interconnection contained in a layout shown bythe layout data 13. FIG. 4 is a conceptual diagram showing the parasiticRC extracting process. A layout of one target interconnection 70 isshown in FIG. 4. This target interconnection 70 includes a firstinterconnection formed in an interconnection layer M1 and a secondinterconnection formed in an interconnection layer M2, for example. Inthe parasitic RC extracting process, the target interconnection 70 isanalyzed, as shown by an arrow in FIG. 4, for example. Here, a patternthat is in accordance with an interconnection structure (cross-sectionalstructure) at each point is selected by referring to the above RClibrary 11. For example, patterns different from each other are selectedfor the first interconnection and the second interconnection. By readingthe RC parameter corresponding to the selected pattern, the parasitic RCrelevant to the target interconnection 70 is calculated. The parasiticRC of all the interconnections is calculated by considering each of theinterconnections in the layout as the target interconnection 70 inorder.

Step S50:

The RC extracting section 32 generates the netlist with parasitic RC 14,by adding the parasitic RC calculated at the step S40, to the netlist12. FIGS. 5A and 5B are conceptual diagrams showing the netlist 12, andthe netlist 14 with parasitic RC, respectively. As an example, FIGS. 5Aand 5B show the netlist 12 and the netlist with parasitic RC 14 relevantto the target interconnection 70 shown in FIG. 4. As shown in FIGS. 5Aand 5B, a parasitic resistance and a parasitic capacitance are added tothe netlist with parasitic RC 14. The RC extracting section 32 outputsthe generated netlist with parasitic RC 14 to be stored in the storageunit 10.

Step S60:

Next, the operation verifying process (the delay verifying process andthe timing verifying process) of the designed LSI are carried out by theverifying tool 40. The verifying tool 40 (the processing unit 20) readsthe netlist with parasitic RC generated at the step S50 from the storageunit 10, and carries out the operation verifying process based on theread-out netlist with parasitic RC 14. When the result of the operationverifying process indicates a “fail” state (step S70: No), the step S20is again carried out. That is, correction of the layout is carried outbased on the verifying process result, and the layout data 13 is againgenerated. After that, the LPE process and the operation verifyingprocess are again carried out. When the result of the operationverifying process indicates a “passed” state (step S70: Yes), the layoutdata 13 generated at the step S20 is adopted as a final layout data.

As would be clarified later, the present invention makes it possible toreduce a process time at the step S40. Also, the number of times toreturn from the step 70 to the step 20 is reduced. As a result, thedesign time of the semiconductor device is greatly reduced. Detaileddescription of the present invention is given below, based on the aboveoverview.

1. Process Variation

First, “process variation” relevant to the present invention will bedescribed in detail. In an actual manufacturing process of asemiconductor device, a structure of an interconnection and so on, maynot be manufactured as precisely as is intended. In other words, across-sectional area (width and thickness) of the interconnection, athickness of an interlayer insulating film, and so on may give variationfrom a desired value. Such a process variation affect the parasitic RCof the interconnection, further affecting a delay.

FIGS. 6A and 6B are conceptual diagrams of cross-sectional structuresshowing the process variation, and shows a “certain pattern” thatincludes the target interconnection 70. FIG. 6A shows a pattern desiredin the design, while FIG. 6B shows a pattern that is actuallymanufactured. In FIGS. 6A and 6B, the target interconnection 70 isformed in the interconnection layer M1, and interconnections 71 a to 71c are formed therearound. The interlayer insulating film 72 is formedbetween the interconnection layers M1 and M2.

As shown in FIG. 6A, a desired width and film thickness of the targetinterconnection 70 are W₀ and T₀, respectively. Also, a desiredthickness and dielectric constant of the interlayer insulating film 72are D₀ and ε₀, respectively. A set of these desired values is referredto as a “center condition” hereinafter. In general, the structure of thesemiconductor device actually manufactured does not perfectly satisfythe center condition. Then, the width and film thickness of the targetinterconnection 70, and the thickness and dielectric constant of theinterlayer insulating film 72 become W, T, D, and ε, respectively, asshown in FIG. 6B. In FIG. 6B, a dotted line indicates the centercondition. The width W and thickness T of the interconnection layer havethe greatest influence among factors relevant to the parasitic RC.Variations of the width W and the thickness T from the center conditiondiffer according to a chip. Therefore, a standard deviation σ_(W) of awidth distribution, and a standard deviation σ_(T) of a film thicknessdistribution in the target interconnection 70 in the manufacturing canbe defined. At this time, the width W and the film thickness T areexpressed by the following equations (1) by use of predeterminedcoefficients α_(W) and α_(T).W=W _(O)α_(W)·σ_(W)T=T _(O)+α_(T)·σ_(T)  (1)Each of the coefficients α_(W) and α_(T) can take a value in a range of−A to +A. The value A is 3, for example. At this time, the width W isexpressed in a range of ±3σ_(W) (a range of 99.7%) from a central valueW₀, which is statistically enough. The same is applied to the filmthickness T. A case where the coefficient α_(W) is ±A corresponds to acase where the width W varies to a maximum extent. Also, a case wherethe coefficient α_(T) is ±A corresponds to a case where the filmthickness T varies to a maximum extent.

According to the present invention, correlation mentioned below isconsidered for the width W and the film thickness T.

Correlation 1:

A correlation does not exist between the width W variation and the filmthickness T variation with respect to a certain interconnection. Inother words, an event “width W variation” and an event “film thickness Tvariation” are independent of each other. That is to say, thecoefficients α_(W) and α_(T) are variables independent of each other.This could be understood from the fact that a process of determining thethickness of an interconnection layer and a process of determining thewidth of the interconnection are separate in a general manufacturingprocess of the semiconductor device. For example, as shown in FIGS. 6Aand 6B, the width W of the target interconnection 70 is larger than thecenter condition W₀, but the film thickness T is smaller than the centercondition T₀.

Correlation 2:

A correlation exists between the width W variation of theinterconnection with respect to the same interconnection layer. Thiscould be understood from the fact that an interconnection is formed byusing a mask and etching in the general manufacturing process of thesemiconductor device. For example, when the width W of the targetinterconnection 70 is larger than the center condition W₀ in theinterconnection layer M1, the width of the interconnection 71 a is alsoincreased as shown in FIGS. 6A and 6B. Also, a correlation existsbetween the film thickness T variations of the interconnection withrespect to the same interconnection layer. This could be understood fromthe fact that the interconnection layer is formed by using a CMP(Chemical Mechanical Polishing) process in the general manufacturingprocess of the semiconductor device. For example, when the filmthickness T of the target interconnection 70 is smaller than the centercondition T₀ in the interconnection layer M1, the thickness of theinterconnection 71 a is also decreased as shown in FIGS. 6A and 6B.

Correlation 3:

A correlation does not exist between the width W variations of theinterconnection with respect to a different interconnection layers.Also, a correlation does not exist between the film thickness Tvariations of the interconnection with respect to the differentinterconnection layers. This could be understood from the fact that thedifferent interconnection layers are formed in different processes inthe general manufacturing process of the semiconductor device. Forexample, the width W of the target interconnection 70 formed in theinterconnection layer M1 is larger than the center condition W₀, whilethe width of the interconnection 71 b formed in the interconnectionlayer M2 is smaller than the center condition, as shown in FIGS. 6A and6B. Also, the film thickness T of the target interconnection 70 formedin the interconnection layer M1 is smaller than the center condition T₀,while the film thickness of the interconnection 71 b formed in theinterconnection layer M2 is larger than the center condition.

2. Building-Up of the RC Library

Next, the building-up of the RC library 11 according to the presentinvention, namely, the step S10 in FIG. 2 will be described in detail.The RC library 11 stores an RC parameter under a “plurality ofconditions” for a single pattern. In addition to the above centercondition, the plurality of conditions include a condition for theprocess variation. Here, factors relevant to the process variation arevarious, and it is not practical to consider all the combinations of thefactors. Since the result of the LPE process is used for the delayverifying process, it is just necessary to know only the conditions inwhich a delay is maximized and minimized (referred to as a “cornerconditions” hereinafter), among the process variation.

FIG. 7 is a diagram showing a method of determining the cornerconditions according to the present invention. In FIG. 7, the horizontalaxis and the vertical axis show the width W and the film thickness T ofthe interconnection (the target interconnection 70), respectively. Anorigin O shows the center condition (W₀, T₀). In FIG. 7, therefore, adistance from the origin O indicates the “process variation”. Byreferring to the equations (1), a coordinate of a point P on the planein FIG. 7 is expressed as (α_(W)σ_(W), σ_(T)σ_(T)). As stated above,each of the coefficients α_(W) and α_(T) can take a value of −3 to +3,for example. At this time, the width W is expressed in a range of±3σ_(W) (range of 99.7%) from the center condition W₀, which isstatistically enough. The same is applied to the film thickness T.

A case where the coefficient α_(W) is ±3 corresponds to a case where thewidth W varies to a maximum extent. Also, a case where the coefficientα_(T) is ±3 corresponds to a case where the film thickness T varies to amaximum extent. It should be noted here as stated above, that thecorrelation does not exist between the width W variation and the filmthickness T variation, and that the coefficients α_(W) and α_(T) are thevariables independent of each other (the correlation 1). This means thata probability P that both of the width W and the film thickness T varyto a maximum extent at the same time (α_(W)=±3, α_(T)=±3) is extremelysmall. For examples, variation shown by the point Q (+3σ_(W), +3σ_(T))in FIG. 7 is overly negative. If such an extreme case is taken intoconsideration, it is necessary to generate a layout data that supportsthe extreme case. This means increase in the number of times torepetition of a layout generating process and a verifying process, andindicates increase in the TAT. According to the present invention,therefore, the extreme case as mentioned above is excluded fromconsideration, though the process variation is taken into consideration.Such exclusion is referred to as “statistical relaxation” hereinafter,in the specification. More specifically, restriction expressed by thefollowing equation (2) is imposed on the coefficients α_(W) and α_(T).√{square root over (α_(W) ²+α_(T) ²)}=3  (2)In other words, the restriction that a sum of squares of ratios of theprocess variations (α_(W), α_(T)) to the standard deviations isconstant, is imposed to the width W and the film thickness T. Under thisrestriction, it is sufficient that the corner conditions in which thedelay of the target interconnection 70 is maximized and minimized iscalculated. That is, the point P on a circle CIRC in FIG. 7 thatcorresponds to the case where the delay is maximized or minimized issearched through a simulation calculation. As a result, the case whereboth the width W and the film thickness T simultaneously vary to amaximum extent is excluded. In that simulation calculation, otherfactors such as a thickness D and the dielectric constant ε of theinterlayer insulating film 72 are assumed to be the center condition.

FIG. 8 shows one example of the result of the above simulation. In FIG.8, the vertical axis shows a delay time obtained through the simulationfor a certain pattern. The horizontal axis shows an angle θ from the Waxis of the point P (see FIG. 7). As shown in FIG. 8, the delay timechanges in a sine curve form in accordance with the angle θ. In thisexample, the delay time is maximized when θ is 30 degrees, and isminimized when θ is 210 degrees. Therefore, a point P1 (θ is 30 degrees)and a point P2 (θ is 210 degrees) shown in FIG. 9 correspond to thecorner conditions of the simulated pattern. The point P1 in which thedelay is maximized and the point P2 in which the delay is minimized areaway from each other by 180 degrees.

FIG. 10A is a graph showing dependency of the parasitic resistance onthe angle θ, and FIG. 10B is a graph showing dependency of the parasiticcapacitance on the angle θ. In FIG. 10A, the vertical axis shows a ratioβ_(R) of a parasitic resistance calculated through the simulation, tothe parasitic resistance in the center condition (W₀, T₀). Also, in FIG.10B, the vertical axis shows a ratio β_(C) of a parasitic capacitancecalculated through the simulation, to the parasitic capacitance in thecenter condition. The ratios β_(R) and β_(C) are referred to as “cornerratios” hereinafter.

As shown in FIGS. 10A and 10B, the parasitic resistance and theparasitic capacitance relevant to the target interconnection 70 changein a sine curve form to the angle θ. In this example, the parasiticresistance is minimized and the parasitic capacitance is maximized atthe point P1 (θ is 30 degrees). On the other hand, the parasiticresistance is maximized and the parasitic capacitance is minimized atthe point P2 (θ is 210 degrees). The reason why the changes in theparasitic resistance and the parasitic capacitance are opposite is thatthe resistance is expressed as a decreasing function to aninterconnection cross-sectional area, while the capacitance is expressedas an increasing function to the interconnection cross-sectional area.Also, the change in the parasitic resistance shown in FIG. 10A is sameas the change of the parasitic resistance multiplied by the parasiticcapacitance (R multiplied by C). This is because the resistance is moresensitive to the change of the form than the capacitance, as seen fromcomparison of the amplitude of the lines shown in FIGS. 10A and 10B.Additionally, in the pattern of this example, the case where theparasitic resistance is minimized and the parasitic capacitance ismaximized, corresponds to the case where the delay time is maximized(the point P1). Also, the case where the parasitic resistance ismaximized and the parasitic capacitance is minimized, corresponds to thecase where the delay time is minimized (the point P2). This tendencydepends on kinds of patters. In some cases, the correspondence isopposite to the correspondence relation shown in FIGS. 10A and 10B.However, the positions (angles) of the points P1 and P2 do not changeeven if the correspondence is opposite.

According to the present invention as described above, the “statisticalrelaxation” is taken into consideration, and the corner conditions arecalculated in which the delay time is maximized and minimized. In otherwords, the conditions that take process variation into considerationinclude two corner conditions (first and second conditions) at least.Although only the width W and the film thickness T of theinterconnection are taken into consideration in the above description,other factors relevant to the delay time may be considered as well.Examples of the other factors are such as the thickness of theinterlayer insulting film, the dielectric constant of the interlayerinsulating film, and a via-contact resistance. At this time, each of theother factors is set to vary to a maximum extent (±3σ).

FIG. 11 is a table showing the corner conditions in the presentinvention. For example, under the first condition, the width W, and thefilm thickness T are given as α_(W)1·σ_(W), and α_(T) ^(1*σ) _(T), andthe thickness of the interlayer insulating film, the dielectricconstant, and the via-contact resistance are given as −3σ, +3σ, and +3σ,respectively. The coefficients α_(W1) and α_(T1) correspond to the pointP1, for example, and correspond to a case where the parasiticcapacitance is maximized and the parasitic resistance is minimized(C_(max) and R_(min)). Under a third condition, the width W, the filmthickness T, the thickness of the interlayer insulating film, thedielectric constant, and the via-contact resistance are given asα_(W)3*σ_(W), α_(T)3*σ_(T), +3σ, −3σ, and −3σ, respectively. Thecoefficients α_(W3) and α_(T3) correspond to the point P1, andcorrespond to the case where the parasitic capacitance is maximized andthe parasitic resistance is minimized (C_(max), and R_(min). That is,the coefficients α_(W1) and α_(W3) are equal, and the coefficientsα_(T1) and α_(T3) are equal. However, variation of the other factors aredifferent between the first and third conditions. The variation of theother factors are set to one of +3σ or −3σ in the first condition, whilethe variation of the other factors are set to the other in the thirdcondition. Therefore, the calculated parasitic RC are different betweenthe first and third conditions.

Under the second condition, the width W, the film thickness T, thethickness of the interlayer insulating film, the dielectric constant,and the via-contact resistance are given as α_(W)2*σ_(W), α_(T)2*σ_(T),−3σ, +3σ, and +3σ, respectively. The coefficients α_(W2) and α_(T2)correspond to the point P2, for example, and correspond to the casewhere the parasitic capacitance is minimized and the parasiticresistance is maximized (C_(min) and R_(max)) Under a fourth condition,the width W, the film thickness T, the thickness of the interlayerinsulating film, the dielectric constant, and the via resistance aregiven as α_(W4)*σ_(W), α_(T)4*σ_(T), +3σ, −3σ, and −3σ, respectively.The coefficients α_(W4) and α_(T4) correspond to the point P2, andcorrespond to the case where the parasitic capacitance is minimized andthe parasitic resistance is maximized (C_(min) and R_(max)) That is, thecoefficients α_(W2 and α) _(W4) are equal, and the coefficients α_(T2)and α_(T4) are equal. However, variation of the other factors aredifferent between the second and fourth conditions. The variation of theother factors are set to one of +3σor −3σ in the second condition, whilethe variation of the other factors are set to the other in the fourthcondition. Therefore, calculated parasitic RC are different between thesecond and fourth conditions.

In this way, the four corner conditions of the present invention aredetermined. It is sufficient that the parasitic RC is calculated throughsimulation for each of the five conditions of the center condition (thezero condition) and the four corner conditions (the first to fourthconditions). Consequently, the RC library 11 of the present invention isbuilt up.

FIG. 12 is a flow chart briefly showing a building method of the RClibrary 11 in the present invention, and showing the contents includedat the step S10. First of all, a plurality of patterns that include thetarget interconnection 70 (see FIGS. 3A and 3B) are prepared (step S11).Then, one pattern is selected from the plurality of patterns (step S12).Subsequently, a point at which a delay is maximized and minimized issearched under the condition shown by the above equations (1) inconsideration of the statistical relaxation (step S13). Consequently,the four corner conditions are determined (see FIG. 11). Subsequently,the parasitic RC under the center condition is calculated, and theparasitic RC under each of the four corner conditions is calculated(step S14).

Next, an RC parameter showing the calculated parasitic RC is stored inthe RC library 11 (step S15). With respect to the center condition, forexample, the calculated parasitic RC is stored as the RC parameter withno change. On the other hand, with respect to the four cornerconditions, the ratio (corner ratios β_(R) and β_(C)) to the parasiticRC under the center condition is stored as the RC parameter. As aresult, a calculation time in the LPE process is reduced as describedlater. When a calculation process is not completed for all the patters(step S16: No), the above steps S13 to S15 are repeated for patternswhere calculation is not yet completed. If the calculation process iscompleted for all the patterns (step S16: Yes), the RC library 11 of thepresent invention is completed (step S17).

FIG. 13 shows an example of the completed RC library 11. As shown inFIG. 13, the RC library 11 stores the RC parameters (a parasiticcapacitance parameter and a parasitic resistance parameter) for aplurality of patters. Here, one data block is allocated to each of thepatterns, and each data block stores the RC parameter for a plurality ofconditions. That is, the RC library 11 stores the RC parameter under thecenter condition (Center) and the four corner conditions (max, min,max′, and min′) for a single pattern. Under the center condition in apattern No. 1, for example, a capacitance value C1 (center capacitancevalue) is stored as the parasitic capacitance parameter, and aresistance value R1 (center resistance value) is stored as the parasiticresistance parameter. Under the four corner conditions, a corner ratioβ_(C)1 (β_(C)1-1 to β_(C)1-4) is stored as the parasitic capacitanceparameter, and a corner ratio β_(R)1 (β_(R)1-1 to β_(R)1-4) is stored asthe parasitic resistance parameter.

In this way, according to the RC library 11 of the present invention,the process variation is taken into consideration, but is narrowed downto the four corner conditions. Therefore, a memory capacity can besaved. Also, the time for the LPE process is reduced by using the RClibrary 11 built in the above way, as described below. Additionally, theRC library 11 just needs to be carried out only once beforehand, for onetechnology (minimum size). The same RC library 11 is used for all theproducts that are based on the same technology.

3. LPE Process (RC Extracting Process)

Next, the LPE process of the present invention, namely, the step 40 inFIG. 2, will be described in detail. FIG. 14 is a flow chart brieflyshowing the LPE process in the present invention, and shows the contentsincluded at the step S40. In this LPE process, the RC library 11 builtin the above way, is referred to.

First Embodiment

First, one target interconnection 70 is selected from a plurality ofinterconnections included in a layout of an LSI under design (step S41).Subsequently, the RC library 11 shown in FIG. 13 is referred to extracta parasitic RC of the target interconnection 70 under the centercondition Center (step S42). The extracting process of the parasitic RCis built in the method shown in FIG. 4. That is, various patterns isreferred to in order, for one target interconnection 70. For example,FIG. 15 conceptually shows the extracting process of the parasitic RC inthis embodiment. In this example, the target interconnection 70 includesa first interconnection formed in an interconnection layer M1, a secondinterconnection formed in an interconnection layer M2, and a thirdinterconnection formed in an interconnection layer M3. At this time, thecenter capacitance value C1 and the center resistance value R1 in thepattern 1 shown in FIG. 13 are used as parasitic RC relevant to thefirst interconnection, for example. In the same way, the pattern 2 isreferred to extract the parasitic RC of the second interconnection, andthe pattern 3 is referred to extract the parasitic RC of the thirdinterconnection. Thus, the parasitic RC of the target interconnection 70under the center condition is extracted.

Next, a parasitic RC of the target interconnection 70 under the cornerconditions is extracted. More specifically, the corner ratios β_(R) andβ_(C) (RC parameters) are read for each of the plurality of patternsthat are referred to at the step S42 (step S43). For example, cornerratios β_(C)1-1 to β_(C)1-4, and β_(R)1-1 to β_(R)1-4 in the pattern 1are read out. Then, it is selected whether or not a correction processis carried out for the read-out corner ratios (step S44). In the firstembodiment of the present invention, the correction process is notcarried out, and the read-out corner ratios β_(R) and β_(C) are used forthe next calculation with no change (step S44: No). More specifically, aresistance value R (Corner) under a certain corner condition iscalculated by multiplying the center resistance value R (Center)obtained at the step S42 and a certain corner ratio β_(R) together.Also, a capacitance value C (Corner) under a certain corner condition iscalculated by multiplying the center capacitance value C (Center)obtained at the step S42 and a certain corner ratio β_(C) (step S45)R(corner)=β_(R) ·R(center)C(corner)=β_(C) ·C(center)  (3)For example, a case is discussed here, where the parasitic RC under thefirst condition relevant to the target interconnection 70 shown in FIG.15 is calculated. In that case, the calculation shown by the aboveequations (3) is carried out for each of the first to thirdinterconnections. More specifically, the parasitic resistance under thefirst condition is calculated by multiplying the center resistance valueR1 and the corner ratio β_(R)1-1, in case of the first interconnectionin the pattern 1. Also, the parasitic capacitance under the firstcondition is calculated by multiplying the center capacitance value C1and the corner ratio β_(C)1-1. Also, for the second interconnectionadaptable for the pattern 2, the parasitic resistance under the firstcondition is calculated by multiplying the center resistance value R2and the corner ratio β_(R)2-1. Also, the parasitic capacitance under thefirst condition is calculated by multiplying the center capacitancevalue C2 and the corner ratio β_(C)2-1. As for the third interconnectionadaptable for the pattern 3, the parasitic resistance under the firstcondition is calculated by multiplying the center resistance value R3and the corner ratio β_(R)3-1. Also, the parasitic capacitance under thefirst condition is calculated by multiplying the center capacitancevalue C3 and the corner ratio β_(C)3-1. The same process is carried outfor the other corner conditions (the second to fourth conditions) aswell. Thus, the parasitic RC of one target interconnection 70 under thefour corner conditions is extracted.

It has already been carried out at the step S42, which of the pluralityof patterns stored in the RC library 11 is adaptable for aninterconnection. At the step S45, therefore, it is not necessary tocarry out a matching process of interconnection and any of the pluralityof patterns stored in the RC library 11. Additionally, it is possible tocalculate the parasitic RC under the four corner conditions with theeasy calculation shown by the equations (3), since the RC parameterrelevant to the four corner conditions is stored in the form of thecorner ratios β_(R) and β_(C). Therefore, the load on a computer isreduced, and a calculation speed is improved.

When the RC extracting process is not yet completed for all theinterconnections included in the layout (step S46: No), anotherinterconnection is set as the target interconnection 70, and the stepsS42 to S45 are repeated. If the RC extracting process is completed forall the interconnections included in the layout (step S46: Yes), the LPEprocess is finished.

As described above, according to the present invention, variousconditions showing the process variation are narrowed down to the abovefirst to fourth conditions. At the step S50 shown in FIG. 2, therefore,only four kinds of the netlists with parasitic RC 14 are generated inone LPE process. Then, it is sufficient that at the step S60, the delayverifying process is carried out only to the four kinds of the netlistswith parasitic RC 14. Consequently, the times for one LPE process anddelay verifying process are reduced. That is to say, reduction in thedesign time of the semiconductor device is realized.

Further, according to the present invention, the “statisticalrelaxation” is taken into consideration when the RC parameter under thefirst to fourth conditions is calculated. That is, a case that aprobability is statistically very low is excluded from the processvariation. Since it is not necessary to support unnecessary cases, afail rate in the delay verifying process can be reduced. Because of thereduction in the fail rate of the delay verifying process, the number oftimes to correct the layout and again carry out the delay verifyingprocess is greatly reduced. In other words, the number of times torepeat the layout process and the verifying process is greatly reduced,since it is not necessary to generate the layout data 13 that supportsextreme cases. Therefore, the TAT can be reduced, and the design time ofthe semiconductor device is reduced.

Second Embodiment

According to the second embodiment of the present invention, acorrection process to be mentioned later is carried out to the cornerratios β_(R) and β_(C) read out at the above step S43 shown in FIG. 14(step S47). As a result of the correction process, a correction ratioβ_(R)′ is derived from the corner ratio β_(R), and a correction ratioβ_(C)′ is derived from the corner ratio β_(C). Then, by using thederived correction ratios β_(R)′ and β_(C)′, the parasitic RC of thetarget interconnection 70 under the corner conditions is extracted. Morespecifically, a resistance value R (Corner) under a certain cornercondition is calculated by multiplying the center resistance value R(Center) obtained at the step S42 and a certain correction ratio β_(R)′.Also, a capacitance value C (Corner) under the certain corner conditionis calculated by multiplying the center capacitance value C (Center)obtained at the step S42 and a certain correction ratio β_(C)′ (stepS45).R(corner)=β_(R) ′·R(center)C(corner)=β_(C) ′·C(center)  (4)In the second embodiment, the correction ratios β_(R)′ and β_(C)′ aregiven by the following equations (5) by use of predetermined correctionparameters γ_(R) and γ_(C).β_(R)′=1+(β_(R)−1)·γ_(R)β_(C)′=1+(β_(C)−1)·γ_(C)  (5)The correction parameters γ_(R) and γ_(C) are determined based on theidea of the “statistical relaxation”, as shown below. FIG. 16 is aconceptual diagram showing the extracting process of a parasitic RC inthe second embodiment. In FIG. 16, a node 80 includes an interconnectionelement 81 formed in an interconnection layer M1, an interconnectionelement 82 formed in an interconnection layer M2, and an interconnectionelement 83 formed in an interconnection layer M3. Here, a node means agroup of interconnections electrically connected. In the node 80, theinterconnection elements 81 to 83 are connected in series. The lengthsof the interconnection elements 81 to 83 are L1, L2, and L3,respectively. A data on the interconnection length can be obtained froman interconnection length data 15 stored in the storage unit 10.According to the present invention, the “statistical relaxation” iscarried out based on the structure of the node 80, and the correctionparameters γ_(R) and γ_(C) are determined.

As stated above, in case of different interconnection layers, there isno correlation between variations of the widths W of theinterconnections, and between variations of the film thicknesses T ofthe interconnections (correlation 3). That is, “independence” existsbetween interconnection layers. Therefore, a probability that a delay ismaximized and minimized in all the interconnection layers at the sametime, is considered to be extremely small. In other words, it is overlynegative to consider that the corner conditions are satisfied in all theinterconnection layers at the same time. In FIG. 16, for example, theinterconnection elements 81 to 83 are arranged in differentinterconnection layers M1 to M3, respectively. Therefore, it is notnecessary to apply the above corner conditions to all theinterconnection elements 81 to 83. According to the present invention,relaxation of the corner conditions is carried out based on theindependence between the interconnection layers.

Here, calculation of a parasitic capacitance will be discussed. In eachinterconnection layer, a parasitic capacitance per unit length isassumed to be given as a common value C₀. Also, in each interconnectionlayer, a corner ratio β_(C) is assumed to be given as a common value β.Although such assumption is not always satisfied in reality, an errorderived from this assumption is considered not to be large. What affectsthe change in delay is a long interconnection. However, various patternsexist in the long interconnection and the changes in delay are averaged.Therefore, the above assumption is likely to be satisfied in case of thelong interconnection. Under the assumption, a total of parasiticcapacitance C_(tot) under the center condition is given asC_(tot)=C₀*(L1+L2+L3). On the other hand, the total of parasiticcapacitance C_(tot) under the corner conditions is given asC_(tot)=β*C₀*(L1+L2+L3). A change in capacitance that results from theinterconnection layers M1 to M3 is given as ΔC1=C₀*(β−1)*L1,ΔC2=C₀*(β−1)*L2, and ΔC3=C₀*(β−1)*L3, respectively. Since theindependence exists between the respective interconnection layers, atotal of the changes is statistically given as the following:(ΔC1² +ΔC2² +ΔC3²)^(1/2)/(ΔC1+ΔC2+ΔC3)=C ₀*(β−1)*γ_(C)That is to say, in the example shown in FIG. 16, the correctionparameters γ_(R) and γ_(C) are given by the following equation (6).$\begin{matrix}{\gamma_{R} = {\gamma_{C} = \frac{\sqrt{{L\quad 1^{2}} + {L\quad 2^{2}} + {L\quad 3^{2}}}}{{L\quad 1} + {L\quad 2} + {L\quad 3}}}} & (6)\end{matrix}$As seen from the equation (6), the correction parameters γ_(R) and γ_(C)are larger than 0 and smaller than 1. When all the interconnectionlengths L1 to L3 are equal, the correction parameters γ_(R) and γ_(C)are 0.58. Therefore, as seen from the equation (5), the correction ratioβ_(R)′ is smaller than the corner ratio β_(R)′ and the correction ratioβ_(C)′ is smaller than the corner ratio β_(C). This means that thecorner conditions are relaxed. That is, variation resulting from thecenter conditions to be considered, can be further reduced. The cornerconditions originally obtained based on the statistical relaxation inthe first embodiment, can be further reduced in the second embodiment.Since it is not necessary to support unnecessary cases, the fail rate inthe delay verifying process is further reduced. Consequently, the numberof times to repeat the layout process and verifying process can befurther reduced.

More generally, it is assumed that the node 80 includes aninterconnection group in each of N layers (N is a natural number) ofinterconnection layers. The interconnection group in a certaininterconnection layer may include a plurality of interconnectionelements. It is assumed that a sum of the lengths of interconnectionelements in an interconnection group in each interconnection layer, isgiven as Li (i is an integer number equal to or larger than 1, and equalto or smaller than N). At this time, the correction parameters γ_(R) andγ_(C) are given as the following equation (7). $\begin{matrix}{\gamma_{R} = {{\gamma\quad}_{C} = {\sqrt{\sum\limits^{N}L_{i}^{2}}/{\sum\limits^{N}L_{i}}}}} & (7)\end{matrix}$FIGS. 17A and 17B are conceptual diagrams showing an example of thecorrection process. In FIG. 17A, a node includes nine interconnectiongroups arranged to the first interconnection layer M1 to the ninthinterconnection layer M9. The sum of the lengths of interconnectionelements in each interconnection group is equal. In this case, thecorrection parameters γ_(R) and γ_(C) are calculated to be 0.33, fromthe above equation (7). In FIG. 17B, a node includes two interconnectiongroups arranged in the first interconnection layer M1 and the secondinterconnection layer M2. A ratio of the sum of the lengths ofinterconnection elements in the interconnection group arranged in thefirst interconnection layer M1, to the sum of the lengths ofinterconnection elements in the interconnection group arranged in thesecond interconnection layer M2, is assumed to be 2:1. In this case, thecorrection parameters γ_(R) and γ_(C) are calculated to be 0.75 from theequation (7). Effect of the statistical relaxation is more apparent inthe example of FIG. 17A than in the example of FIG. 17B. This is becausea case where variation are maximized “at the same time” in all the nineindependent interconnection groups is practically very rare.

FIG. 18 is a conceptual diagram showing another example of thecorrection process in this embodiment. In FIG. 18, a branching point ispresent in the node 80. More in detail, the node 80 includesinterconnection elements 85 to 87. The interconnection elements 85 and86 are connected in series through the connecting node 84. Also, theinterconnection elements 85 and 87 are connected in series through theconnecting node 84. The interconnection elements 86 and 87 are connectedin parallel. Each length of the interconnection elements 85 to 87 isgiven as L1 to L3, respectively.

In this case, the correction parameter γ_(C) for the parasiticcapacitance is given by the same equation as the above equation (6) or(7). However, the correction parameter γ_(R) for the parasiticresistance is different for each of the interconnection elements. Morespecifically, as for a line that includes the interconnection elements85 and 86, the existence of the interconnection element 87 is ignored,and the correction parameter γ_(R) is given as γ_(R)(a) in the followingequations (8). On the other hand, as for a line that includes theinterconnection elements 85 and 87, the existence of the interconnectionelement 86 is ignored, and the correction parameter γ_(R) is given asγ_(R)(b) in the following equations (8). $\begin{matrix}{{{\gamma_{R}(a)} = \frac{\sqrt{{L\quad 1^{2}} + {L\quad 2^{2}}}}{{L\quad 1} + {L\quad 2}}}{{\gamma_{R}(b)} = \frac{\sqrt{{L\quad 1^{2}} + {L\quad 3^{2}}}}{{L\quad 1} + {L\quad 3}}}} & (8)\end{matrix}$As for the interconnection elements 85 located on the uppersteam sidefrom the connecting point 84, two kinds of correction parametersγ_(R)(a) and γ_(R)(b) are calculated as candidates. In this case, thelarger one of the two correction parameters is adopted as the correctionparameter γ_(R) relevant to the interconnection element 85. Thus, whenthe connecting node is provided in the node 80, the correction parameterγ_(R) is calculated separately for each of the lines connected inseries. For example, when all the interconnection lengths L1 to L3 areequal in the example shown in FIG. 18, the correction parameter γ_(R)for the parasitic resistance is 0.71, respectively.

More generally, it is assumed that the node 80 includes aninterconnection group in each of N (N is a natural number)interconnection layers. In the node 80, a certain line is assumed toinclude a “sub interconnection group” connected in series in n (n is aninteger number equal to or larger than 1, and equal to or smaller thanN) interconnection layers. Also, it is assumed that a sum of the lengthsof the interconnection elements in the interconnection group is given asLj (j is an integer number equal to or larger than one, and equal to orsmaller than n). At this time, the correction parameter γ_(R) for theline is given by the following equation (9). $\begin{matrix}{\gamma_{R} = {\sqrt{\sum\limits^{n}L_{j}^{2}}/{\sum\limits^{n}L_{j}}}} & (9)\end{matrix}$FIG. 19 shows a structure of another node 80. This node 80 includesinterconnection elements 90 to 99. The lengths of the interconnectionelements 90 to 99 are all equal. In the node 80, the interconnectionelements 90 and 94 to 96 are arranged in a first interconnection layerM1. The interconnection elements 91 and 97 to 99 are arranged in asecond interconnection layer M2. The interconnection elements 92 and 93are arranged in a third interconnection layer M3. Therefore, a ratio ofthe sum of the lengths of the interconnection elements in theinterconnection group in each of the interconnection layers M1 to M3 is2:2:1. Consequently, the correction parameter γ_(C) for the parasiticcapacitance is calculated to be 0.6 based on the above equation (6) or(7). Also, the correction parameter γ_(R) for the parasitic resistanceis calculated for each of the lines based on the above equation (9).When a plurality of correction parameters γ_(R) are calculated for acertain interconnection element, the largest one of the plurality ofcorrection parameters is selected. As a result, a distribution of thecorrection parameters γ_(R) shown in FIG. 19 can be obtained.

FIG. 20 is a conceptual diagram showing another example of thecorrection process in this embodiment. In FIG. 20, a first node 101includes an interconnection arranged in an interconnection layer M1, anda second node 102 includes the first interconnection arranged in theinterconnection layer M1 and a second interconnection arranged in aninterconnection layer M2. In the first node 101, the correctionparameter γ_(C) for the parasitic capacitance is calculated to be 1.00.In the second node 102, the correction parameter γ_(C) for the parasiticcapacitance is calculated to be 0.71. At this time, the largercorrection parameter 1.00 is adopted for a coupling capacitance 110between the first node 101 and the second node 102. That is, the largestamong a plurality of correction parameters γ_(C) calculated for eachnode, is adopted for a coupling capacitance between nodes.

By using the correction parameters γ_(R) and γ_(C) described above, thecorner ratios β_(R) and β_(C) are corrected, and the correction ratiosβ_(R)′ and β_(C)′ are calculated (see the equation (5)). Then, by usingthe calculated correction ratios β_(R)′ and β_(C)′, the parasitic RCunder the corner conditions is calculated (see FIG. 16 and the equation(4)). Thus, the LPE process in this embodiment is carried out.

According to the second embodiment, the same effect as that of the firstembodiment can be attained. Further, according to the second embodiment,the “statistical relaxation” is further carried out for a corner ratioβ. As a result, the fail rate in the delay verifying process is furtherreduced. Consequently, the TAT can be further reduced, and the designtime of the semiconductor device can be further reduced.

According to the design technique of the semiconductor device of thepresent invention, the number of a plurality of conditions showingprocess variation is limited. In particular, the conditions that showthe process variation are narrowed down to the four conditions which arenecessary and sufficient. As a result, a time for one LPE process isreduced. That is to say, reduction in the design time of thesemiconductor device is realized.

Further, according to the design technique of the semiconductor deviceof the present invention, a case that has statistically very lowprobability among the process variation is excluded in carrying out theLPE process. That is, the “statistical relaxation” is applied to the LPEprocess. Since it is not necessary to support unnecessary cases, thefail rate in the delay verifying process is reduced. The number of timesto correct a layout and again perform the delay verifying process isgreatly reduced, since the fail rate in the delay verifying process isreduced. That is, the TAT can be reduced, and the reduction in thedesign time of the semiconductor device can be realized.

Further, according to the manufacturing method of the semiconductordevice of the present invention, it is possible to prevent an overmargin of the design, since the method of the statistical relaxation isused, and variation of an interconnection delay time is estimatedthrough exclusion of conditions that seem rare as actual manufacturingconditions. It is also possible to expect a high manufacturing yield andprovide a high-quality semiconductor device, since variation ofmanufacturing conditions that seem possible in reality are take intoconsideration.

That is to say, when layout design of a semiconductor device is carriedout, a design rule and manufacturing conditions (requirementspecifications for a manufacturing process for satisfying the designrule) of the semiconductor device are usually determined in advance. Thedesign rule includes minimum patterns of an interconnection width,interconnection space, and so on. Thus, it is determined in advance, towhich extent of variation interconnection width, capacitance filmthickness, layer resistance value, and dielectric constant should bemanufactured. In carrying out the layout design of the semiconductordevice, an interconnection pattern is determined based on the designrule such that functional specifications of the semiconductor device tobe designed are realized. Generally, if the layout design of thesemiconductor device is seemingly completed, manufacturing variation ofthe semiconductor device is considered, and variation of actualinterconnection delay is estimated from the layout pattern. Then, asimulation is carried out to see whether or not the predeterminedfunctions are realized. According to the present invention, it ispossible to conduct the simulation under the consideration of actualmanufacturing variation. Then, the pattern is formed on a semiconductorsubstrate to manufacture the semiconductor device in accordance with theverified layout pattern, by use of known methods. Consequently, it ispossible to prevent an over margin of the layout design, and realize aspace-saving layout, since variation of manufacturing conditions rare inreality are excluded. At the same, it is possible to expect a highmanufacturing yield, and provide a high-quality semiconductor device,since the layout pattern takes variation of manufacturing conditionspossible in reality, into consideration.

According to a semiconductor device design technique of the presentinvention, the number of a plurality of conditions showing processvariation is limited. In particular, conditions showing the processvariation are narrowed down to four conditions which are necessary andsufficient. Consequently, the time taken for one LPE process is reduced.That is, reduction in a design time of the semiconductor device isrealized.

Further, according to the semiconductor device design technique of thepresent invention, the LPE is carried out with exclusion of a case thatis statistically very low in probability among the process variation.That is to say, “statistical relaxation” is applied to the LPE. Since itis not necessary to support unnecessary cases, a fail rate in the delayverifying process is reduced. Because of the reduction in the fail ratein the delay verifying process, the number of times to correct thelayout and again perform the delay verifying process is greatly reduced.In other words, TAT (Turn Around Time) is reduced, realizing a reductionin the design time of the semiconductor device.

1. A computer-readable software product comprising codes, executed by acomputer, for a method of determining parasitic resistance andcapacitance from a layout of an LSI, said method comprising: providing aplurality of patterns of a wiring structure which contains a targetinterconnection; and producing a library configured to store parametersindicating said parasitic resistance and said parasitic capacitance inrelation to said target interconnection to each of said plurality ofpatterns, wherein said producing comprises: calculating said parametersto a plurality of conditions corresponding to deviation in manufactureof said wiring structure for each of said plurality of patterns.
 2. Thesoftware product according to claim 1, wherein said plurality ofconditions comprises a 0^(th) condition to a second condition, a desiredwidth and desired film thickness of said target interconnection are W₀and T₀, respectively, standard deviations of a distribution of saidwidth of said target interconnection and a distribution of said filmthickness thereof are σ_(W) and σ_(T), respectively, and said width Wand said film thickness T in actual manufacture of said targetinterconnection are expressed, by using coefficients α_(W) and α_(T), asW=W ₀α_(W)*σ_(W)andT=T ₀+α_(T)*α_(T), said 0^(th) condition is a case where said width Wand said film thickness T are W₀ and T0, respectively, said firstcondition is a case where a delay in said target interconnection ismaximized under a condition that α_(W) ²+αT² is constant, and saidsecond condition is when the delay in said target interconnection isminimized under the condition that α_(W) ²+αT² is constant.
 3. Thesoftware product according to claim 2, wherein in case of said firstcondition, one of said parasitic resistance of and said parasiticcapacitance related to said target interconnection is maximized, and theother is minimized, and in case of said second condition, said one isminimized and the other is maximized.
 4. The software product accordingto claim 2, wherein said plurality of conditions further contains athird condition and a fourth condition, a deviation of another factorwhich relates to said delay is ranged from +σ₀ to −σ₀, said firstcondition is the case where said delay is maximized under the conditionthat the deviation of said another factor is one of +σ₀, and −σ₀ andα_(W) ²+α_(T) ² is constant, said third condition is the case where saiddelay is maximized under the condition that the deviation of saidanother factor is the other of +σ₀ and −σ₀ and σ_(W) ²+α_(T) ² isconstant, said second condition is the case where said delay isminimized under the condition that the deviation of said another factoris one of +σ₀ and −σ₀ and α_(W) ²+α_(T) ² is constant, and said fourthcondition is the case where said delay is minimized under the conditionthat the deviation of said another factor is the other of +σ₀ and −σ₀and α_(W) ²+α_(T) ² is constant.
 5. The software product according toclaim 4, wherein said coefficients α_(W) and α_(W) in said firstcondition are equal to said coefficients α_(W) and α_(T) in said thirdcondition, and said coefficients α_(W) and α_(T) in said secondcondition are equal to said coefficients α_(W) and α_(T) in said fourthcondition.
 6. The software product according to claim 4, wherein in saidlibrary, a center resistance value as a value of said parasiticresistance and a center capacitance value as a value of said parasiticcapacitance are stored as said parameter to said 0th condition, and aratio β_(R) of said parasitic resistance to said center resistance and aratio β_(C) of said parasitic capacitance to said center capacitancevalue are stored as said parameter to each of said first to fourthconditions.
 7. The software product according to claim 1, wherein saidmethod further comprises: reading a netlist of said LSI; reading alayout data indicating said layout of said LSI; calculating saidparasitic resistance and said parasitic capacitance in each of saidplurality of conditions to each of said interconnections contained insaid layout by referring to said parameters stored in said library; andgenerating a netlist with parasitic RC by adding the calculatedparasitic resistance and the calculated parasitic capacitance to saidnetlist.
 8. The software product according to claim 6, wherein saidmethod further comprises: reading a netlist of said LSI; reading alayout data indicating said layout of said LSI; calculating saidparasitic resistance and said parasitic capacitance in each of saidplurality of conditions to each of said interconnections contained insaid layout by referring to said center resistance value, said centercapacitance value, and the ratios β_(R) and β_(C) stored in saidlibrary; and generating a netlist with parasitic RC by adding thecalculated parasitic resistance and the calculated parasitic capacitanceto said netlist.
 9. The software product according to claim 8, whereinsaid calculating comprises: calculating said parasitic resistance andsaid parasitic capacitance in each of said first to fourth conditions bymultiplying the ratios β_(R) and β_(C) by said center resistance valueand said center capacitance value, respectively.
 10. The softwareproduct according to claim 8, wherein said calculating comprises:generating correction ratios β_(R)′ and β_(C)′ by correcting said ratiosβ_(R) and β_(C) based on a configuration of a node; and calculating saidparasitic resistance and said parasitic capacitance in each of saidfirst to fourth conditions by multiplying the correction ratios β_(R)′and β_(C)′ by said center resistance value and said center capacitancevalue, respectively.
 11. The software product according to claim 10,wherein said node comprises a group of interconnections in each of Ninterconnection layers (N is a natural number), a summation of lengthsof the interconnections in said group is Li (i is an integer equal to ormore than 1 and equal to or smaller than N), said ratio β_(C) and saidcorrection ratio β_(C)′ are the following equation:β_(C)′=1+(β_(C)−1)γ_(C) a parameter γ_(C) satisfies the followingequation:$\gamma_{C} = {\sqrt{\sum\limits^{N}L_{i}^{2}}/{\sum\limits^{N}L_{i}}}$12. The software product according to claim 11, wherein saidinterconnection groups are connected in series in said node, said ratioβ_(R) and said correction ratio β_(R)′ are the following equation:β_(R)′=1+(β_(R)−1)γ_(R) said parameter γ_(R) satisfies the followingequation:$\gamma_{R} = {\sqrt{\sum\limits^{N}L_{i}^{2}}/{\sum\limits^{N}L_{i}}}$13. The software product according to claim 11, wherein saidinterconnection groups is branched in said node, a sub interconnectiongroup in n interconnection layer (n is an integer equal to or more than1 and equal to or smaller than N) is connected in series to oneinterconnection in said interconnection group, a summation of lengths ofthe interconnections in said sub interconnection group is Lj (j is aninteger equal to or more than 1 and equal to or smaller than n), saidratio β_(R) and said correction ratio β_(R)′ to said one interconnectionare the following equation:β_(R)′=1+(β_(R)−1)γ_(R) said parameter γ_(R) satisfies the followingequation:$\gamma_{R} = {\sqrt{\sum\limits^{n}L_{j}^{2}}/{\sum\limits^{n}L_{j}}}$14. The software product according to claim 13, wherein when a pluralityof said correction ratios β_(R)′ are calculated to said oneinterconnection, the largest one of said plurality of correction ratiosβ_(R)′ is adopted.
 15. The software product according to claim 11,wherein the largest one of a plurality of said correction ratios β_(C)′is adopted as a coupling capacitance between said nodes.
 16. Acomputer-readable software product comprising codes, executed by acomputer, for a method of determining parasitic resistance andcapacitance from a layout of an LSI, by referring a library, wherein awiring structure which contains a target interconnection is a pattern,and said library stores parameters indicating said parasitic resistanceand said parasitic capacitance in relation to said targetinterconnection to a plurality of conditions for variation inmanufacture of said wiring structure with respect to each of a pluralityof said patterns, said method comprising: reading a netlist of said LSI;reading a layout data indicating said layout of said LSI; calculatingsaid parasitic resistance and said parasitic capacitance in each of saidplurality of conditions to each of said interconnections contained insaid layout by referring to said parameters stored in said library; andgenerating a netlist with parasitic RC by adding the calculatedparasitic resistance and the calculated parasitic capacitance to saidnetlist.
 17. The software product according to claim 16, wherein adesired width and desired film thickness of said target interconnectionare W₀ and T₀, respectively, standard deviations of a distribution ofsaid width of said target interconnection and a distribution of saidfilm thickness thereof are σ_(W) and α_(T), respectively, and said widthW and said film thickness T in actual manufacture of said targetinterconnection are expressed, by using coefficients α_(W) and α_(T), asW=W ₀+α_(W)*σ_(W)andT=T ₀+α_(T)*σ_(T), said plurality of conditions comprises a 0^(th)condition to a second condition, said 0^(th) condition is a case wheresaid width W and said film thickness T are W₀ and T0, respectively, saidfirst condition is a case where a delay in said target interconnectionis maximized under a condition that α_(W) ²+α_(T) ² is constant, andsaid second condition is when the delay in said target interconnectionis minimized under the condition that α_(W) ²+α_(T) ² is constant. 18.The software product according to claim 17, wherein said plurality ofconditions further contains a third condition and a fourth condition, adeviation of another factor which relates to said delay is ranged from+σ₀ to −σ₀, said first condition is the case where said delay ismaximized under the condition that the deviation of said another factoris one of +σ₀ and −σ₀ and α_(W) ²+α_(T) ² is constant, said thirdcondition is the case where said delay is maximized under the conditionthat the deviation of said another factor is the other of +σ₀ and −σ₀and α_(W) ²+α_(T) ² is constant, said second condition is the case wheresaid delay is minimized under the condition that the deviation of saidanother factor is one of +σ₀ and −σ₀ and α_(W) ²+α_(T) ² is constant,and said fourth condition is the case where said delay is minimizedunder the condition that the deviation of said another factor is theother of +σ₀ and −σ₀ and α_(W) ²+α_(T) ² is constant.
 19. The softwareproduct according to claim 18, wherein in said library, a centerresistance value as a value of said parasitic resistance and a centercapacitance value as a value of said parasitic capacitance are stored assaid parameter to said 0th condition, and a ratio β_(R) of saidparasitic resistance to said center resistance and a ratio β_(C) of saidparasitic capacitance to said center capacitance value are stored assaid parameter to each of said first to fourth conditions.
 20. A methodof manufacturing a semiconductor device which has a plurality of wiringlayers, comprising: determining design criteria, and a manufacturingcondition of said semiconductor device; carrying out layout design ofsaid semiconductor device based on functional specification and saiddesign criteria to produce a layout data; estimating process variationsof width and thickness of each of interconnections for every wiringlayer from said layout data based on said design criteria and saidmanufacturing condition; determining an interconnection delay affectedby a specific condition of said process variations for every wiringlayer; repeating correction of said layout data, the estimation and thedetermination until the determined interconnection delay meets saidfunction specification, to produce a final layout data; andmanufacturing said semiconductor device based on said final layout dataand said manufacture condition, wherein said determining aninterconnection delay comprises: determining a variation of saidinterconnection delay by using of parasitic resistance and parasiticcapacitance for every wiring layer through statistical relaxation inwhich the process variations of width and thickness of each ofinterconnections are independent between said plurality of wiringlayers.